Updated: Thursday, October 24th, 2013 at 10:07pm

BRUSSELS – European leaders united in anger Thursday as they attended a summit overshadowed by reports of widespread U.S. spying on its allies – allegations German Chancellor Angela Merkel said had shattered trust in the Obama administration and undermined the crucial trans-Atlantic relationship.

The latest revelations that the U.S. National Security Agency swept up more than 70 million phone records in France and may have tapped Merkel’s own cellphone brought denunciations from the French and German governments.

Merkel’s unusually stern remarks as she arrived at the European Union gathering indicated she wasn’t placated by a phone conversation she had Wednesday with President Barack Obama, or his personal assurances that the U.S. is not listening in on her calls now.

“We need trust among allies and partners,” Merkel told reporters in Brussels. “Such trust now has to be built anew. This is what we have to think about.”

“The United States of America and Europe face common challenges. We are allies,” the German leader said. “But such an alliance can only be built on trust. That’s why I repeat again: spying among friends, that cannot be.”

The White House may soon face other irked heads of state and government. The British newspaper The Guardian said Thursday it obtained a confidential memo suggesting the NSA was able to monitor 35 world leaders’ communications in 2006. The memo said the NSA encouraged senior officials at the White House, Pentagon and other agencies to share their contacts so the spy agency could add foreign leaders’ phone numbers to its surveillance systems, the report said.

The Guardian did not identify who reportedly was eavesdropped on, but said the memo termed the payoff very meager: “Little reportable intelligence” was obtained, it said.

Other European leaders arriving for the 28-nation meeting echoed Merkel’s displeasure. Swedish Prime Minister Fredrik Reinfeldt called it “completely unacceptable” for a country to eavesdrop on an allied leader.

If reports that Merkel’s cellphone had been tapped are true, “it is exceptionally serious,” Dutch Prime Minister Mark Rutte told national broadcaster NOS.

“We want the truth,” Italian Premier Enrico Letta told reporters. “It is not in the least bit conceivable that activity of this type could be acceptable.”

Echoing Merkel, Austria’s foreign minister, Micheal Spindelegger, said, “We need to re-establish with the U.S. a relationship of trust, which has certainly suffered from this.”

France, which also vocally objected to allies spying on each other, asked that the issue of reinforcing Europeans’ privacy in the digital age be added to the agenda of the two-day summit.